Rechargeable battery and method for fabricating the same

ABSTRACT

An inorganic solid electrolytic rechargeable battery capable of offering excellent battery characteristics is disclosed. The battery has positive and negative electrodes and an inorganic electrolyte interposed therebetween. The positive and negative electrodes are each made up of an active material layer and a current collector layer. The positive electrode collector layer or the negative electrode collector layer is a conductive metal oxide layer. The negative electrode active material layer is made of lithium metals or lithium alloys. This negative active layer may alternatively be made of a material which causes an operation voltage potential of the negative electrode to become more noble than 1.0 V with respect to the potential of a metallic lithium. A complexity-reduced fabrication method of the rechargeable battery is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2004-289946, filed on Oct. 1,2004, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rechargeable battery using aninorganic solid electrolyte and a fabrication method thereof.

2. Related Art

As the quest grows for downsizing and weight-saving of electronicequipment, electrochemical storage battery cells also are more stronglydemanded to satisfy such small-size/light-weight requirements. Toachieve a battery which fully meets these requirements, ultra-small andultra-thin batteries are under consideration, which are evolved from theintegration or “collaboration” of thin-film architectures and batterymaterial technologies. These thickness-reduced or “slim” batteries areexpected to be used as power sources for integrated circuit (IC) cardsand IC tags or to be mounted on large-scale integration (LSI) chipsubstrates.

On the other hand, high-power rechargeable batteries have been broughtinto practical use, including currently available lithium-ionrechargeable or secondary batteries having in combination a positiveelectrode made of lithium cobaltate, a negative electrode made of carbonmaterial, and an electrolysis solution with lithium salts beingdissolved in a nonaqueous solvent. While these are manufactured byvarious methods, one major approach for reduction to practice is toemploy a process which includes the steps of depositing positive andnegative electrode materials as slurried respectively, dehydratingresultant layers or membranes, cutting or “dicing” them into portions ofa prespecified shape, rolling them under pressure, winding, andinjecting thereinto an electrolysis solution. Unfortunately, such priorknown methodology having these steps is encountered with limits tobattery thinning and miniaturization.

Consequentially, in order to make batteries smaller and thinner, alow-profile solid-state electrolyte secondary battery has been proposed,which has its negative electrode made of metallic lithium or carbon, apositive electrode made of LiCoO₂ or LiMn₂O₄, and an electrolyte elementmade of inorganic solid electrolyte material. The battery of this typeis manufacturable by using semiconductor processes, such as sputtering,deposition or else, in combination with patterning techniques. Some ofsuch battery are disclosed, for example, in Published UnexaminedJapanese Patent Application Nos. JP-A-2000-106366 and 2004-127743.

As the prior known solid electrolyte batteries are fabricated bythin-film fabrication processes, such as sputter techniques, thesebatteries suffer from problems as to an increase in time consumed forfilm fabrication, difficulty in film lamination, and an increase inproduction costs. Another problem faced with the prior art solidelectrolyte batteries is that since these are often designed to employfor the electrolyte certain metals such as copper, aluminum, gold,palladium or other similar high-conductivity metals, any intendedthermal processing after film fabrication is incapable of beingsufficiently performed. This is a serious bar to the achievement ofexcellent crystallinity of active material, resulting in the batterycharacteristics becoming deficient and inacceptable for practical use.

BRIEF SUMMARY OF THE INVENTION

This invention has been made in view of the problems stated above, andits object is to provide a rechargeable battery which is manufacturableby simplified processes and which is excellent in batterycharacteristics and thus adaptable for miniaturization and thicknessreduction, along with a method of making such rechargeable battery.

In accordance with a first aspect of the invention of the devicecategory, a rechargeable battery—say, a “first” rechargeable battery—isprovided which includes positive and negative electrodes and a solidelectrolyte layer which contains lithium. The positive electrode has apositive active material layer and a positive current collector layer.The negative electrode has a negative active material layer, which istypically made of a metallic lithium or lithium alloy, and a negativecollector layer. The inorganic solid electrolyte layer is interposedbetween the positive and negative electrodes. At least one of thepositive and negative electrode collector layers is comprised of aconductive metal oxide.

In accordance with a second aspect of the device-category invention, a“second” rechargeable battery includes a positive electrode having apositive active material layer and a positive collector layer, and anegative electrode having a negative active material layer and anegative collector layer. The negative active material layer iscomprised of a negative active material which causes an operationvoltage potential of the negative electrode to become more noble than1.0 volt (V) with respect to a potential of metallic lithium. Thebattery also includes a lithium-containing inorganic solid electrolytewhich is laminated between the positive and negative electrodes. Atleast one of the positive and negative collector layers comprises aconductive metal oxide.

In accordance with a first aspect of the invention of the methodcategory, a first rechargeable battery fabrication method is provided,which includes the steps of forming a multilayer structure having asequential lamination of a positive electrode current collector layer, apositive electrode active material layer, a lithium-containing inorganicsolid electrolyte layer and a negative electrode collector layer,sintering the multilayer structure in an oxidizable atmosphere, andperforming, after the sintering, electrical charge-up of the multilayerstructure to thereby create between the negative collector layer and theinorganic solid electrolyte layer a negative electrode active materiallayer which is made of either a metallic lithium or a lithium alloy. Atleast one of the positive and negative collector layers comprises aconductive metal oxide.

In accordance with a second aspect of the method-category invention, asecond rechargeable battery fabrication method includes laminating apositive collector layer, a positive active material layer, alithium-containing inorganic solid electrolyte layer, a negative activematerial layer and a negative collector layer to thereby obtain amultilayer structure thereof. The negative active material layercomprises a negative active material with an operation voltage potentialof the negative electrode becoming more noble than 1.0V with respect toa potential of metallic lithium. The method also includes sintering themultilayer structure in an oxidizable atmosphere. At least one of thepositive and negative collector layers comprises a conductive metaloxide.

An important feature of the first and second rechargeable batteries andthe first and second fabrication methods of the invention is that aconductive metal oxide is used for either the positive electrode or thenegative electrode current collector while using a specifically chosennegative electrode active material. This conductive metal oxide hardlyexhibits any appreciable change in quality due to heating—in particular,heat application in oxidizable atmospheres. Thus it is possible tofabricate battery elements by use of currently available sinteringtechniques. In addition, owing to selection of the specific negativeactive material, the reversibility of absorption and release of lithiumions is excellent while retaining an extended cycle life of the battery.

According to the invention, it is possible to provide a rechargeablebattery which is manufacturable by complexity-reduced methodology whileoffering excellent battery characteristics and thus is suitable forthin-shape designs.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram schematically showing a cross-sectional view of arechargeable battery embodying the invention.

FIG. 2 illustrates, partly in cross-section, some major process steps ofa rechargeable battery fabrication method also embodying the invention.

DETAILED DESCRIPTION OF THE INVENTION

Intense studies are conducted by the inventors in terms of the preferredform of a secondary battery capable of being prepared by a simplifiedprocess without damaging the battery characteristics to reveal the factwhich follows. When utilizing an inorganic solid electrolyte for theelectrolyte and also using conductive metal oxides for either thepositive electrode current collector or the negative electrode collectorin combination with the co-use of a specific negative electrode activematerial, it becomes possible to obtain the intended rechargeablebattery by sintering together those battery element precursors havingthe positive and negative electrodes and inorganic solid electrolyte.This makes it possible to prepare, at low costs, a small-size batterywhile reducing complexities in fabrication process and facility, whencompared to prior known battery manufacturing methods using traditionalfilm fabrication techniques, such as sputtering or else. It was alsofound that the obtained rechargeable battery's respective constituentmembers increase in density, resulting in each member exhibitingsufficient ion conduction property and electrical conductivity, therebyenabling obtainment of sufficiently enhanced battery characteristics.

Referring to FIG. 1, a lithium-ion rechargeable or secondary battery inaccordance with an embodiment of this invention is depicted incross-section. Note that this illustrative embodiment incorporates theprincipal features of the first and second rechargeable batteries of theinvention, which will be set forth in detail below.

An explanation will first be given of common structural features to thefirst and second rechargeable batteries.

As shown in FIG. 1, a battery cell is arranged to have a unitarymultilayer structure of a positive electrode 1, a negative electrode 2and an inorganic solid electrolyte layer 3. The positive and negativeelectrodes 1-2 oppose each other with the electrolyte layer 3 interposedtherebetween. The positive electrode 1 has a positive electrode activematerial layer 4 and a positive electrode current collector layer 5,which are laminated on each other. The negative electrode 2 has alamination of a negative electrode active material layer 6 and anegative collector layer 7. The inorganic solid electrolyte layer 3 issandwiched between these positive and negative electrodes 1-2. Outerelectrodes 8 and 9 having electrical wiring leads for deriving an outputto external circuitry associated therewith are stacked on the positiveand negative electrodes 1-2, respectively. The illustrative laminatestructure is particularly adaptable for use as a thin or “slim” battery.The positive electrode active layer 4 is designed for example to have athickness which preferably ranges from 500 to 0.1 micrometer (μm)—morepreferably, 50 to 1 μm. The positive collector layer 5 preferably has athickness of 500 to 0.1 μm, more preferably, 50 to 1 μm, The inorganicsolid electrolyte layer 3 is preferably 500 to 0.1 μm thick, morepreferably 50 to 1 μm. The negative electrode active layer 6 has ispreferably 500 to 0.1 μm thick, more preferably, 50 to 1 μm. Thenegative electrode collector layer 7 is preferably 500 to 0.1 μm thick,more preferably 50 to 1 μm. The positive electrode active material layer4 of positive electrode 1 is arranged as follows. This positive activelayer 4 may be made of various kinds of positive active materialsincluding, but not limited to, metal oxides and metal sulfides. Inparticular, in case metal oxides are used, it becomes possible toperform the sintering of rechargeable battery in oxygen-containingatmospheres. This in turn makes it possible for resultant rechargeablebatteries to obtain an active material that is less in oxygen defectsand yet high in crystallinity. Thus, the use of metal oxides isdesirable for fabrication of a large-capacity battery having its currentcapacity in close proximity to a theoretically expected capacity.

A practically employable example of the positive electrode activematerial is at least one kind of material as selected from the groupconsisting essentially of manganese dioxide (MnO₂), iron oxide, copperoxide, nickel oxide, lithium-manganese composite oxide (for example,Li_(x)Mn₂O₄ or Li_(x)MnO₂), lithium-nickel composite oxide (e.g.,Li_(x)NiO₂), Lithium-cobalt composite oxide (Li_(x)CoO₂),Lithium-nickel-cobalt composite oxide (e.g., LiNi_(1-y)CO_(y)O₂),lithium-manganese-cobalt composite oxide (e.g., LiMn_(y)Co_(1-y)O₂),spinel type lithium-manganese-nickel composite material(Li_(x)Mn_(2−y)Ni_(y)O₂), lithium phosphorus oxide of the type having anolivine structure (such as Li_(x)FePO₄, Li_(x)Fe_(1−y)Mn_(y)PO₄,Li_(x)CoPO₄ or else), iron sulfate (Fe₂(SO₄)₃), and vanadium oxide(e.g., V₂O₅). Note that the suffixes “x” and “y” as used in thesechemical formulas are preferably determined fall within a range of 0 to1.

More preferable examples of the positive active material are highbattery voltage-attainable lithium manganese composite oxide(Li_(x)Mn₂O₄), lithium nickel composite oxide (Li_(x)NiO₂), lithiumcobalt composite oxide (Li_(x)CoO₂), lithium nickel cobalt compositeoxide (Li_(x)Ni_(1−y)Co_(y)O₂), spinel type lithium manganese nickelcomposite oxide (Li_(x)Mn_(2−y)Ni_(y)O₄), lithium manganese cobaltcomposite oxide (Li_(x)Mn_(y)Co_(1−y)O₂), and lithium iron phosphate(Li_(x)FePO₄). Note that the suffixes x and y are preferably arranged torange from 0 to 1. These positive active materials are improved incrystallinity by sintering in oxidizable atmospheres, which leads toimprovements in battery characteristics.

In regard to the positive electrode current collector layer 5 andnegative electrode collector layer 7, at least one of these collectorlayers 5 and 7 used here is a conductive metal oxide layer. Theconductive metal oxide layer refers to the one that has conductive metaloxides unified together into the form of a layer or membrane. This mayalso be a porous composition having in the layer ultrafine holes orvoids. Using this material makes it possible to sinter all of theelectrodes and electrolyte plus collectors at a time, thereby permittingresultant active materials to become higher in crystallinity. Thisfurther improves the electrical conductivities thereof. Thus, thisapproach is extremely suitable for obtaining excellent batteryproperties.

In cases where such conductive metal oxide is not used for either one ofthe positive and negative collector layers 5 and 7, it is permissible touse collector elements made of metals, such as copper or nickel, ormetal alloys which hardly react with lithium ions at charge/dischargepotentials of the negative electrode. However, this approach is notpreferable because of the fact that such materials readily react withpositive and negative active layers during high-temperature sinteringafter film formation, resulting in risks as to degradation of thebattery characteristics. It is especially desirable to use conductivemetal oxide layers for both the positive collector layer 5 and thenegative collector layer 7.

The above-noted conductive metal oxide may typically be at least onekind of element as selected from the group consisting of tin (Sn),indium (In), zinc (Zn), and titanium (Ti). More specifically, SnO₂,In₂O₃, ZnO and TiO_(x) (where x is greater than or equal to 0.5 and yetless than or equal to 2) may be good examples of the metal oxide. When aneed arises, these conductive metal oxides may be designed to containtherein a limited amount—for example, 10 atomic percent (at %) orless—of conductivity enhancing elements, such as antimony (Sb), niobium(Nb), tantalum (Ta) or else.

Regarding the inorganic solid electrolyte layer 3, this layer may bemade of a specific material that inherently has ionic conductivity andis negligibly less in electron conductivity. The inorganic solidelectrolyte 3 is designed to contain lithium, so an ultimately obtainedrechargeable battery is such that lithium ions act as movable ions.Preferable examples are Li₃PO₄, nitrogen-admixed Li₃PO₄ (0<x≦1), lithiumion-conductible hyaline or vitreous solid electrolyte such as Li₂S—SiS₂,Li₂S—P₂S₅, Li₂S—B₂S₃ or else, and lithium ion-conductable solidelectrolyte made of these vitreous materials doped with a lithiumhalide, such as LiI or else, and/or a lithium oxyacid, such as Li₃PO₄.These are effective because of their high lithium ion conductivities. Ofthese materials, lithium/titanium/oxygen-containing titanium oxide-basedsolid electrolyte—for example, Li_(x)La_(y)TiO₃ (where, 0<x<1 and 0<y<1)or the like—must be a preferable material because this exhibits stableperformance even during sintering in oxygen gaseous atmospheres.

As for the outer electrodes 8-9, these may be made of known conductivematerials; for example, silver (Ag), alloys of Ag and palladium (Pd),nickel (Ni)-plated or deposited copper (Cu), or equivalents thereto.Optionally, solder plating may be applied to outer electrode surfacesfor parts mounting purposes. An electrical connection form of the outerelectrodes 8-9 should not exclusively be limited to the one shown inFIG. 1, and may alternatively be arranged so that a battery structurehaving the positive and negative electrodes 1-2 and inorganic solidelectrolyte layer 3 is covered or coated with resin material or else,while using lead wires for connection to portions of the positive andnegative electrodes to derive outputs toward the outside.

It should be noted that main components of the secondary battery—i.e.,the positive electrode 1, negative electrode 2 to be later discussed,inorganic solid electrolyte 3, and outer electrodes 8-9—may be modifiedto contain therein certain inorganic substance, such as for exampleSiO₂, Al₂O₃, PbO, MgO and others or, alternatively, contain organicsubstance such as polyvinyl-butyral (PVB), metyl-ethyl-ketone (MEK) orelse.

Although in regard to the shape of rechargeable battery an exemplarysecondary battery of the planar type having a multilayer of flatlayer-shaped electrodes and electrolyte is shown in FIG. 1, the batteryshape is not limited thereto. Other possible examples are batteries ofthe type having column- or rod-like shapes.

An explanation will next be given of an active material for use as thenegative electrode active layer 6, which is not the common structuralfeature to the first and second rechargeable batteries of the invention.By applying the negative electrode active material for use in the firstand second batteries, the negative active material properties thereofare hardly deteriorated even when using methodology for fabricatingrechargeable batteries by sintering together several battery elementprecursors. This ensures that resultant products offer excellent batterycharacteristics.

(1) First Rechargeable Battery

In the first rechargeable battery, the negative active material for useas the negative active layer 6 is made of a metallic lithium or lithiumalloy. The lithium alloy may be an alloy of lithium and at least oneselected from the group consisting of Sn, In and Zn. This alloy ispreferable since this is large in current capacity, thus enablingthinning or “slimming” of resultant battery structures while at the sametime suppressing creation of stresses at interfaces. Typical examples ofsuch alloy composition are Li_(4.4)Sn, LiIn, LiZn and equivalentsthereof. In particular, Li_(4.4)Sn is desirable as it has a highcapacity and is capable of being made thinner.

The negative active layer 6 made of the metal lithium or the lithiumalloy is formable by segregation in an initial charge-up event after theassembly of a rechargeable battery. In case the conductive metal oxidemaking up the negative current collector layer 7 is a material thatreacts with lithium ions as released from either the positive activelayer 4 or the inorganic solid electrolyte layer 3 (e.g., tin oxides,indium oxides, zinc oxides, etc.), a layer of lithium alloy whichultimately becomes the negative active layer 6 is formed between theinorganic solid electrolyte layer 3 and the negative collector layer 7.Alternatively, in case the conductive metal oxide making up the negativecollector layer 7 is a material that hardly reacts with lithium ionsreleased from the positive electrode (e.g., titanium oxides), a metallithium layer that becomes the negative active layer 6 is formed betweenthe inorganic solid electrolyte layer 3 and negative collector layer 7.The negative active layer 6 to be formed by such chargeup in this waycomes with the formation of a good interface, which is rich inattachability or adhesivity with its neighboring membrane, such as theinorganic solid electrolyte layer 3 or the negative collector layer 7.This makes it possible to manufacture excellent batteries less ininterface resistance.

(2) Second Rechargeable Battery

The negative active material used for the negative active layer 6 in thesecond rechargeable battery is the specific one that an operationvoltage potential of the negative electrode 2 becomes more noble than1.0V with respect to the potential of the metal lithium. The conductivemetal oxide used for the negative collector layer 7 is less than orequal to 1.0V in potential for intercalation and desorption of lithiumions. Accordingly, the conductive metal oxide of negative collectorlayer 7 no longer behaves to react with lithium ions at the potentialwhereat the lithium-ion intercalation/desorption progresses in thenegative active layer 6. This ensures that the reaction of theconductive metal oxide of collector layer 7 hardly impedes electrodereactions of the negative active material per se. This would result inimprovement of battery cycle life, when compared to the first batterystated above.

Desirably, the negative active material used here is a carefully chosenmaterial that permits the negative electrode's operation voltagepotential to be more noble than 1.0V with respect to the metal lithium'spotential, while at the same time having electrical conductivity andbeing high in reversibility of lithium-ion intercalation/desorptionreactions, and further stays less in volume change uponabsorption/storage and release of lithium ions and also does notsignificantly change in quality due to heat application. Some majorexamples of the material are metal oxides and metal sulfides, such astungsten oxides (for example, WO_(a), where 1.8<a<2.2, with the negativeelectrode operation potential ranging from 1.0 to 1.4V), molybdenumoxides (e.g., MoO_(b), where 1.8<b<2.2, and the negative electrodeoperation potential of 1.0 to 1.4V), iron sulfides (e.g., Fe_(c)S where0.9<c<1.1 and the negative electrode operation potential ofapproximately 1.8V), lithium iron sulfides (Li_(x)FeS_(y) where 0≦x≦4.0and 0.9≦y≦2.1 with the negative electrode operation potential of about1.8V), titanium sulfides (e.g., TiS_(d) where 1.8<b<2.2 and the negativeelectrode operation potential of 1.5 to 2.7V), and lithium titanates(e.g., Li_(4+z)Ti₅O₁₂ where 0≦z≦3 and the negative electrode operationpotential of about 1.55V). These are employable in sole or incombination of more than two of them. In particular, it is desirable touse composite sulfides which contain therein both lithium and iron oruse composite oxides containing lithium and titanium. More desirably, aniron sulfide represented by Li_(x)FeS_(y) (0≦x≦4, 0.9≦y≦2.1) with thenegative electrode operation potential of about 1.8V or a lithiumtitanate of the type having the spinel structure defined by the chemicalformula Li_(4+x)TiSO₁₂ (0≦x≦3) with the negative electrode operationpotential of about 1.55V is used, because such is great in lithium-ionabsorption/storage amount and thus enables achievement of increasedbattery capacity.

As apparent from the foregoing, it is possible by using the arrangementsof the first and second rechargeable batteries to employ fabricationprocesses for sintering together the positive and negative electrodesand the inorganic solid electrolyte. Thus it is possible to complete theintended inorganic solid electrolyte rechargeable battery by thefollowing simplified process, by way of example.

An explanation will next be given of a method of fabricating the firstand second rechargeable batteries with reference to FIG. 2. FIG. 2 is adiagram which illustrates, in schematic cross-section, some major stepsof the rechargeable battery fabrication process.

As shown in FIG. 2, prepare on carrier sheets 10 an inorganic solidelectrolyte layer 3, a positive active layer 4, a positive collectorlayer 5, a negative electrode-use active layer 6 and a negative currentcollector layer 7, respectively as an example. Note here that in thecase of a rechargeable battery of the type having its negative activematerial layer to be formed through segregation by initial chargeup at alater step, it is unnecessary to prepare in advance the negative activelayer 6.

The formation of each layer can be performed in a way which follows: usescreen print or doctor blade techniques to deposit a slurry on thecarrier sheet to a required thickness, wherein the slurry comprises aconstituent material of each member as blended and admixed with a binder(for example, polyvinyliden fluoride, stylene butadiene rubber or thelike) and a solvent (e.g., N-methyl pyrrolidone, water or else); and,thereafter, remove the carrier sheet. Desirably, those materials thatbehave to form an electrically insulative layer due to oxidization areprevented from being contained in the positive collector layer 5 andnegative active layer 6 made of conductive metal oxides and from beingcoated on the surfaces of these layers.

As far as the materials making up respective layers are mutuallyinsoluble, a plurality of members may be laminated together incombination on the same carrier sheet; for example, the positive activelayer 4 and positive collector layer 5 are formed by sequentiallystacking them on the same carrier sheet. It is also possible tosequentially laminate by screen print techniques all members of thepositive active layer 4, positive collector layer 5, negative activelayer 6 (this is unnecessary in case this layer is formed by the initialchargeup), negative collector layer 7 and inorganic solid electrolytelayer 3 while letting them be in the state of the slurry stated supra.

Then, remove the carrier sheet from each dehydrated layer. Next, form abattery component precursor by laminating the layers in such a mannerthat the inorganic solid electrolyte layer 3 is interposed between thepositive active layer 4 and negative active layer 6 while causing thepositive collector layer 5 to be positioned outside of the positiveactive layer 4 and also letting the negative collector layer 7 be placedoutside of the negative active layer 6. At this time, it is desirablethat the process be done while thermal compression is applied thereto.Next, put the resulting battery element precursor in a certain jig forunification of respective layers, followed by execution of hydrostaticpressure processing. Thereafter, perform dicing machining.

Furthermore, this battery element precursor is subjected tohigh-temperature sintering at temperatures greater than or equal to 500°C. and yet less than or equal to 1500° C.; preferably, at temperaturesranging from 700 to 900° C. Regarding an atmosphere during sintering,the sintering is done in an oxidizable atmosphere in view of the factthat oxides are used as the layer material. A typical example of it isan oxygen-containing atmosphere. Although it is the simplest way to doit in ambient atmospheres, similar results are also obtainable when theabove process is carried out while adjusting various kinds ofatmospheres in order to adjust of oxidation and reduction (i.e., redox)reactions in a way depending upon the material used. Preferably, a timeperiod for the sintering is set to fall within a range of from 0.1 to 10hours.

Then, attach outer electrodes 8 and 9 for connection to the positive andnegative collector layers 5 and 7, respectively. Next, adhere metallicterminals to outer electrodes 8-9 by welding techniques usingelectrically conductive paste or else, followed by dehydration thereof.Thereafter, the resultant structure is coated by dipping with an outersheath or “shell” due to resin coating and is then hardened, thereby tocomplete the rechargeable battery.

Additionally, in case the negative active layer 6 is formed by theinitial chargeup, a charging process is performed thereafter so that thenegative active layer 6 is segregated between the solid electrolytelayer 3 and negative collector layer 7.

EXAMPLES Example 1

A rechargeable battery, also called secondary battery, was prepared by amethod having the steps which follow. The battery has a unitary laminatestructure such as shown in FIG. 1. Some major process steps in themanufacture of such battery are illustrated in cross-section in FIG. 2.

<Forming Inorganic Solid Electrolyte Layer>

A slurry was prepared by admixture and blend of chosen inorganic solidelectrolytic materials into N-methylpyrrolidone (NMP), which are 95weight percent (wt %) of lantern lithium titanate (Li_(x)La_(y)TiO₃)powder and 5 wt % of polyvinyliden fluoride (PVdF). Then, deposit thisslurry on a carrier sheet 10, followed by dehydration. This resulted inan inorganic solid electrolyte layer 3 being formed on the carrier sheet10.

<Forming Positive/Negative Electrolyte Layers>

A slurry was prepared by mixture and blend of 95 wt % of antimony-dopedtin oxide (SnO₂) powder and 5 wt % of polyvinyliden fluoride (PVdF) intoN-methylpyrrolidone (NMP). Deposit this slurry on carrier sheets 10, andthen dry it, resulting in a positive current collector layer 5 and anegative collector layer 7 being formed on the carrier sheets 10,respectively.

<Forming Positive Active Layer>

A slurry was prepared by mixture and blend of 95 wt % of lithium cobaltoxide (LiCoO₂) powder and 5 wt % of PVdF into NMP. Deposit this slurryon a carrier sheet 10, and then dry it, resulting in a positive activelayer 4 being formed on carrier sheet 10.

Let the positive collector layer 5, positive active layer 4, inorganicsolid electrolyte layer 3 and negative active layer 6 made of theseconstituent members be sequentially laminated to thereby form a batteryelement precursor, which was then sintered in an oxygen gas flow at 900°C. for 1 hour.

After having attached outer electrodes 8-9 for connection to theresultant battery element's positive and negative collector layers 5 and7 respectively, electrically charge it up to 4.1V. Thus, an inorganicsolid electrolyte secondary battery was completed.

The battery completed is then cut or diced vertically relative to itslamination faces. Then, scanning electron microscopy (SEM) andassociated energy dispersive X-ray (EDX) analysis and X-ray diffraction(XRD) analysis were performed. Results of this analyzation welldemonstrated the presence of a layer or membrane of Li—Sn alloy for useas the negative active layer 6 between the negative collector sheet 7and the inorganic solid electrolyte layer 3.

Example 2

A battery was formed, which is similar to that of Example 1 except thatits positive and negative current collector layers are made of an indiumoxide (In₂O₃)

The battery completed is then trimmed or diced vertically relative toits laminate faces. As a result of execution of SEM-EDX analysis and XRDanalysis, there was affirmed the presence of a Li—In alloy layer for useas the negative active layer 6 between the negative collector sheet 7and the inorganic solid electrolyte layer 3.

Example 3

A battery was formed, which is similar to that of Example 1 except thatits positive and negative collector layers are made of zinc oxide (ZnO).

The battery completed is then diced vertically relative to its laminatefaces. Then, SEM-EDX analysis and XRD analysis were done to affirm thepresence of a Li—Zn alloy layer for use as the negative active layer 6between the negative collector sheet 7 and inorganic solid electrolytelayer 3.

Example 4

A battery was formed, which is similar to that of Example 1 except thatits positive and negative collector layers are made of niobium-dopedtitanium oxide (TiO₂).

The battery completed is diced vertically relative to its laminatefaces. Then, SEM-EDX and XRD analyses were done to affirm the presenceof a Li metal layer between the negative collector layer and inorganicsolid electrolyte layer.

Example 5

By using a positive collector layer 5, positive active layer 4,inorganic solid electrolyte layer 3 and negative collector layer 7 whichare similar to those of Example 1 and also using as the negative activelayer 6 a membrane that was formed in a way as described below,sequentially laminate the positive collector layer 5, positive activelayer 4, inorganic solid electrolyte layer 3, negative active layer 6and negative collector layer 7 to thereby form a battery elementprecursor. Let this precursor be sintered in the flow of an oxygen gasat 900° C. for 1 hour.

After having attached outer electrodes 8-9 for connection to theresultant battery element's positive and negative collector layers 5 and7 respectively, charge it up to 2.8V, resulting in completion of aninorganic solid electrolyte secondary battery.

<Forming Negative Active Layer>

A slurry was prepared by mixture and blend of chosen negative activematerials, such as 95 wt % of lithium titanate (Li₄Ti₅O₁₂) powder and 5wt % of PVdF into NMP. Then, deposit this slurry into a sheet-likeshape, followed by dehydration.

Example 6

A battery was formed, which is similar to that of Example 5 except thatits positive and negative collector layers are made of indium oxide(In₂O₃).

Example 7

A battery was formed, which is similar to that of Example 5 except thatits positive and negative collector layers are made of zinc oxide (ZnO).

Example 8

A battery was formed, which is similar to that of Example 5 except thatits positive and negative collector layers are made of niobium-dopedtitanium oxide (TiO₂).

Example 9

A battery was formed, which is similar to Example 5 except that ironsulfide (FeS) is used as its negative active material.

Example 10

A battery was formed, which is similar to Example 5 except that titaniumsulfide (TiS₂) is used as its negative active material.

Example 11

A battery was formed, which is similar to Example 5 except that tungstenoxide (WO₂) is used as its negative active material.

Comparative Example 1

A battery was formed, which is similar to Example 1 except for thefollowing arrangements. A negative active layer 6 was formed on acarrier sheet 10 while using a foil of aluminum for its positivecollector layer 5 and also using a copper foil as a negative collectorlayer 7 and further using black lead or graphite as its negative activematerial, resulting in formation of a battery element precursor.Thereafter, sintering is applied thereto, thus forming the negativeactive layer 6.

Comparative Example 2

A battery was formed, which is similar to Example 1 except for thefollowing: a negative active layer 6 was formed while using an aluminumfoil for the positive collector layer 5 and also using a copper foil asthe negative collector layer 7 and further using graphite as thenegative active material, resulting in formation of a battery elementprecursor. Thereafter, sintering was done in an argon atmosphere, thusforming the negative active layer 6.

Comparative Example 3

A battery was formed, which is similar to Example 1 except for thefollowing: a negative active layer 6 was formed on a carrier sheet 10while using graphite as the negative active material, resulting information of a battery element precursor, which was then subject tosintering, resulting in formation of the negative active layer 6.

Comparative Example 4

A battery was formed, which is similar to Example 1 except that itsnegative collector layer 7 is made of graphite, which was appliedsintering in an argon atmosphere.

Comparative Example 5

A battery was formed, which is similar to Example 1 except that itspositive collector layer 5 is made of an aluminum foil whereas itsnegative collector layer 7 is made of a copper foil.

Measurement results of battery capacity values of Examples 1 to 11 andComparative Examples 1-5 thus completed in the way stated above areindicated in Table 1. As the positive active materials for use inrespective batteries are substantially the same both in kind and indeposition amount, the resulting battery capacities are expected to havethe same value. However, it has been revealed that Comparative Examples1-4 are extremely less in battery capacity than Example 1.

Capacity-measured batteries were then disassembled for analysispurposes, revealing the fact that the battery of Comparative Example 1is such that various different kinds of quality-deteriorated layers wereformed due to oxidation of the graphite for use as the current collectorand negative active material. It is very likely that this poor-qualitylayer creation has lowered the battery characteristics.

Regarding the battery of Comparative Example 2, such oxidation of thegraphite used for its current collector and negative active material wassuppressed and reduced; however, it was found that the lithium cobaltateused for the positive active material decreases in crystallinity. It isconsidered that this crystallinity decrease is due to execution of thesintering in the reducible atmosphere, which in turn causes degradationof the battery properties.

As for the battery of Comparative Example 3, it was observed that thegraphite for use as its negative active material was oxidized in asimilar way to that of Comparative Example 1. In the battery ofComparative Example 4, its positive active material appreciablydecreases in crystallinity as in Comparative Example 2. In the bothcases, the battery performance is degraded.

In the battery of Comparative Example 5, it was affirmed that thealuminum and copper used for its current collectors were oxidized, whichcaused the collapse of collector layers, resulting in a decrease inbattery performance.

Additionally, measurement results of charge/discharge cycle life for thebatteries of Examples 1-11 are also presented in Table 1 below. Cyclelife testing was done at 20° C. while letting charge and dischargecurrents be set to 1C. Regarding the batteries of Examples 1-4, acharging time period was set to 3 hours, with charge and dischargeendpoint voltages being set at 4.1V and 3V, respectively. With suchvalue settings, charge/discharge cycles were repeated to thereby measureresultant capacity retain factors. In regard to the batteries ofExamples 5-11, their capacity retain rates were measured by repeatedexecution of charge/discharge cycles while setting the charge time to 3hours, the charge end voltage to 2.8V, and the discharge end voltage to1.5V.

TABLE 1 Capacity Retainability Cell Capacity After 500 Cycles (μAh) (%)Example 1 100 78 Example 2 100 72 Example 3 100 70 Example 4 100 65Example 5 100 98 Example 6 100 96 Example 7 100 95 Example 8 100 97Example 9 100 88 Example 10 100 85 Example 11 100 80 Comparative  5 —Example 1 Comparative  20 — Example 2 Comparative  10 — Example 3Comparative  30 — Example 4 Comparative  10 — Example 5

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A method of making a rechargeable battery comprising: forming amultilayer structure having a positive collector layer, a positiveactive material layer, a lithium-containing inorganic solid electrolytelayer and a negative collector layer; sintering said multilayerstructure in an oxidizable atmosphere; and charging, after thesintering, of said multilayer structure to create between said negativecollector layer and said inorganic solid electrolyte layer, a negativeactive material layer made of any one of a metallic lithium and alithium alloy, wherein at least one of said positive collector layer andsaid negative collector layer comprises a conductive metal oxide.
 2. Themethod according to claim 1, wherein said conductive metal oxide is anoxide of at least one kind of element as selected from the groupconsisting of Sn, In, Zn and Ti.
 3. The method according to claim 2,wherein said conductive metal oxide is at least one selected from thegroup consisting of SnO₂, In₂O₃, ZnO, and TiO_(x) wherein x is equal toor greater than 0.5 and equal to or less than
 2. 4. The method accordingto claim 3, wherein said lithium alloy comprises lithium and at leastone element selected from the group consisting of Sn, In and Zn.
 5. Themethod according to claim 1, wherein said positive collector layer andsaid negative collector layer comprise the conductive metal oxide.
 6. Amethod for making a rechargeable battery comprising: forming amultilayer structure having a positive collector layer, a positiveactive material layer, a lithium-containing inorganic solid electrolytelayer, a negative active material layer and a negative collector layer,said negative active material layer comprising a negative activematerial with an operation voltage potential of a negative electrodebecoming more noble than 1.0V with respect to a potential of metalliclithium; and sintering said multilayer structure in an oxidizableatmosphere, wherein at least one of said positive collector layer andsaid negative collector layer comprises a conductive metal oxide.
 7. Themethod according to claim 6, wherein said conductive metal oxide is anoxide of at least one kind of element as selected from the groupconsisting of Sn, In, Zn and Ti.
 8. The method according to claim 7,wherein said conductive metal oxide is at least one selected from thegroup consisting of SnO₂, In₂O₃, ZnO and TiO_(x) wherein x is equal toor greater than 0.5 and equal to or less than
 2. 9. The method accordingto claim 6, wherein the negative active material causing the negativeoperation voltage potential to become more noble than 1.0V with respectto the metallic lithium potential is at least one selected from thegroup consisting of tungsten oxide, molybdenum oxide, iron sulfide,lithium iron sulfide, titanium sulfide and lithium titanate.
 10. Themethod according to claim 6, wherein said positive collector layer andsaid negative collector layer comprise the conductive metal oxide.